1. Field of Invention
This invention relates to a light emitting device that is provided with LED elements and emits white light.
2. Description of Related Art
A light emitting device has conventionally been known that emits white light by combining an LED element and fluorescent material (see, e.g., Japanese Patent Application Publication No. 2003-535478 and corresponding U.S. Pat. No. 6,504,179). The light emitting device described in this document is provided with an LED element that emits radiation of 300-470 nm and generates white light as a result of this radiation being converted into light having a longer wavelength fully or partially by the fluorescent material excited by this radiation. The fluorescent material is dispersed in sealing resin that seals the LED element.
A light emitting device has also been known that can generate white light by combining a red LED element, a green LED element and a blue LED element (See, e.g., Japanese Laid-open Application No. 2008-085324). However, in the light emitting device described in Japanese Patent Application Publication No. 2003-535478 and corresponding U.S. Pat. No. 6,504,179, the heat resistance of the fluorescent material is low in the sealing resin, and the emission efficiency of the light emitting device declines when the temperature of the device increases when in use. Moreover, since the heat quantity of an LED element is restricted, it is difficult to increase luminous flux by flowing a high electric current to the LED element.
As shown in the light emitting device described in Japanese Laid-open Application No. 2008-085324, it may be possible to generate white light using red, green and blue LED elements in place of a fluorescent material. However, the full width at half maximum of each LED element is extremely small compared with that of a fluorescent material, the color rendering of white light generated declines. Furthermore, in the case that the heat quantity of an LED element is not restricted, it becomes necessary to smoothly transmit heat generated at each element to a substrate on which the element is carried.